Cured gels including polyurethane gels have long been used to seal electrical components and to protect metallic structures from corrosion, for example, by sea-water. For example, polyurethane gels have been cast in place around multiconductor cable joints by mixing the gel forming components (di- or polyisocyanates and hydroxy-terminated polybutadienes or polyesters) and a diluent and then pouring the mixture quickly around the joint and allowing it to cure in place. The curing of polyisocyanate/diol mixtures is relatively slow (for example, several days even with catalyst added) at room temperature. In recent years, as disclosed inter alia in U.S. Pat. Nos. 4,600,261 and 4,634,207 (Debbaut), the disclosures of which are incorporated herein by reference for all purposes, articles comprising precured gels have been used to protect electrical contacts and other substrates.
Other known uses for gels include the insulation of busbars and other electrical components using silicone gels and non-silicone gels, especially butyl gels as described by Chang and Toy in EP 0174165 (1986) and by Toy in EP 0229102 (1987), which describes, inter alia, the use of such gels as insulating and stress grading compositions in high voltage terminations and connectors. The disclosure of each of these applications is incorporated herein by reference.
The polyurethane gels used by the prior art have excellent short term physical properties but have poor aging resistance, i.e. they are poor in such long term chemical and physical properties as hydrolytic and thermal stability, resistance to moisture and resistance to compression set especially at higher temperatures within the anticipated service range. In addition, polyurethane gels can under certain circumstances extract plasticizer from, or otherwise impair the functionality of, poly(vinyl chloride) insulation.